Site Problem

Dear All,
I have been optimizing a website for last 8 months and now its ranking is good. Its Page Rank was 3. Today I checked my website ranking in SERP and found url without www in SERPs and when I checked the site crawling then it shows last crawling date is oct 4, and after 3 or 4 hour when I checked once again that page then I shocked:
=> Page Rank showing is 0 ( earlier it was 3)
=> Cached Version not showing (before 3 hours it was)

Note:
This problem occurs in homepage only all other pages have no effect.